The present invention relates generally to chucks for use with drills or with electric or pneumatic power drivers. More particularly, the present invention relates to jaws for use with such chucks.
Both hand and electric or pneumatic tool drivers are well known. Although twist drills are the most common tools on such drivers, the tools may also comprise screw drivers, nut drivers, burrs, mounted grinding stones, and other cutting or abrading tools. Since the tool shanks may be of varying diameter or of polygonal cross section, the device is usually provided with a chuck adjustable over a relatively wide range. The chuck may be attached to the driver by a threaded or tapered bore.
A variety of chucks have been developed in the art. In an oblique jawed chuck, a chuck body includes three passageways disposed approximately 120° apart from each other. The passageways are configured so that their center lines meet at a point along the chuck axis forward of the chuck. The passageways constrain three jaws which are moveable in the passageways to grip a cylindrical or polygonal tool shank displaced approximately along the chuck center axis. The chuck includes a nut that rotates about the chuck center and that engages threads on the jaws so that rotation of the nut moves the jaws in either direction within the passageways. The body is attached onto the drive shaft of a driver and is configured so that rotation of the body in one direction with respect to the nut forces the jaws into gripping relationship with the tool shank, while rotation in the opposite direction releases the gripping relationship. The chuck may be keyless if it is rotated by hand. Examples of such chucks are disclosed in U.S. Pat. Nos. 5,125,673 and 5,193,824, commonly assigned to the present assignee and the entire disclosures of which are incorporated by reference herein. Various configurations of keyless chucks are known in the art and are desirable for a variety of applications.
As noted above, drill bits typically have shanks that are either cylindrical or of a polygonal cross section. Typically, for those applications wherein a large diameter accessory on the end of the drill bit is required, the drill bit shank will be of a polygonal cross section to help provide a more secure hold of the drill bit by the jaws of the chuck. For example, self-feeding drill bits and drill bits used to create conduits through joists for piping and electrical wiring often have polygonal shanks.
A typical jaw face configuration for holding such drill bits in a standard quarter-inch chuck is shown in FIG. 1. Each jaw face includes one or more teeth that meet at a pointed apex for engaging a flat sidewall 53 of the polygonal drill bit shank 51. During drilling operations, it is possible for torque exerted on the drill bit to cause shank 51 to work back and forth within the jaws, thereby developing a looseness. Continued drilling operations in this condition often leads to the apexes of the jaw teeth disrupting material on the shank of the drill bit. Eventually, the shank of the drill bit is destroyed and the drill bit can no longer be used.
Another known jaw face configuration is shown in FIG. 2. In order to prevent damage to shank 51 of the drill bit, each jaw face is planar over the width of the corresponding sidewall 53 it engages. As such, the jaw face does not disrupt the material of the shank. However, because the width of each jaw face is approximately equal to the width of the corresponding shank sidewall, during drilling operations, it is not uncommon for the torque exerted on the drill bit to cause the jaws to rotate within their respective jaw passageways. Such rotation may cause the jaws to become so tight on shank 51 of the drill bit that the user cannot loosen the chuck without excessive force.
The present invention recognizes and addresses the foregoing considerations, and others, of prior art constructions and methods.